Theophylline

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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C₇H₈N₄O₂ · H₂O 198.18

C₇H₈N₄O₂ 180.17

1H-Purine-2,6-dione, 3,7-dihydro-1,3-dimethyl-, monohydrate;

Theophylline monohydrate CAS RN®: 5967-84-0; UNII: C137DTR5RG.

Anhydrous CAS RN®: 58-55-9; UNII: 0I55128JYK.

1 DEFINITION

Theophylline contains one molecule of water of hydration or is anhydrous. It contains NLT 97.0% and NMT 102.0% of theophylline (C₇H₈N₄O₂ ), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020)

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Solution A: 10 mM ammonium acetate prepared as follows. Transfer 770.8 mg of ammonium acetate to a 1-L volumetric flask, and dissolve in 80% flask volume of water. Adjust with glacial acetic acid to a pH of 5.5 and dilute with water to volume. Pass through a suitable filter of 0.2-μm pore size.

Solution B: Methanol

Mobile phase: See Table 1.

Table 1

System suitability solution: 1 mg/mL of USP Theophylline RS and 1 μg/mL of USP Theophylline Related Compound F RS, from Impurity stock

solution, in water. Sonicate as needed to aid in the dissolution.

Standard solution: 0.2 mg/mL of USP Theophylline RS in water

Sample solution: 0.2 mg/mL of Theophylline in water

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 270 nm

Column: 2.1-mm × 10-cm; 1.7-μm packing L1

Column temperature: 40°

Flow rate: 0.4 mL/min

Injection volume: 1 μL

System suitability

Samples: System suitability solution and Standard solution.

[Note—See Table 2 for the relative retention times.]

Suitability requirements

Resolution: NLT 1.5 between theophylline and theophylline related compound F, System suitability solution

Relative standard deviation: NMT 0.73%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of theophylline (C₇H₈N₄O₂ ) in the portion of Theophylline taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of theophylline from the Sample solution

r_S = peak response of theophylline from the Standard solution

C_S = concentration of USP Theophylline RS in the Standard solution (mg/mL)

C_U = concentration of Theophylline in the Sample solution (mg/mL)

Acceptance criteria: 97.0%–102.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.15%

Organic Impurities

Solution A, Solution B, Mobile phase, Impurity stock solution, and System suitability solution: Proceed as directed in the Assay.

Standard stock solution: 50 μg/mL each of USP Caffeine RS, USP Theophylline RS, USP Theophylline Related Compound B RS, USP

Theophylline Related Compound C RS, USP Theophylline Related Compound D RS, and USP Theophylline Related Compound F RS

Standard solution: 1 μg/mL each of USP Caffeine RS, USP Theophylline RS, USP Theophylline Related Compound B RS, USP Theophylline

Related Compound C RS, USP Theophylline Related Compound D RS, and USP Theophylline Related Compound F RS, from Standard stock solution, in water

Sample solution: 1.0 mg/mL of Theophylline in water

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector

For unspecified impurities with absorption maxima near 220 nm: UV 220 nm

For specified impurities and unspecified impurities with absorption maxima near 270 nm: UV 270 nm

Column: 2.1-mm × 10-cm; 1.7-μm packing L1

Column temperature: 40°

Flow rate: 0.4 mL/min

Injection volume: 1 μL

System suitability

Samples: System suitability solution and Standard solution

[Note—See Table 2 for relative retention times.]

Suitability requirements

Resolution: NLT 1.5 between theophylline and theophylline related compound F, System suitability solution

Relative standard deviation: NMT 3.0% for each peak present in the Standard solution

Analysis

Samples: Standard solution and Sample solution

For impurities detected at 270 nm

Calculate the percentage of caffeine, theophylline related compound B, theophylline related compound C, and theophylline related

compound D in the portion of Theophylline taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of caffeine, theophylline related compound B, theophylline related compound C, or theophylline related compound D from the Sample solution

r_S = peak response of the corresponding Reference Standard from the Standard solution

C_S = concentration of USP Caffeine RS, USP Theophylline Related Compound B RS, USP Theophylline Related Compound C RS, or USP Theophylline Related Compound D RS in the Standard solution (mg/mL)

C_U = concentration of Theophylline in the Sample solution (mg/mL)

Calculate the percentage of any other individual unspecified impurity with absorption maxima near 270 in the portion of Theophylline taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of any other individual unspecified impurity from the Sample solution

r_S = peak response of theophylline from the Standard solution

C_S = concentration of USP Theophylline RS in the Standard solution (mg/mL)

C_U = concentration of Theophylline in the Sample solution (mg/mL)

For impurities detected at 220 nm

Calculate the percentage of any other individual unspecified impurity with absorption maxima near 220 in the portion of Theophylline taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of any other individual unspecified impurity from the Sample solution

r_S = peak response of theophylline from the Standard solution

C_S = concentration of USP Theophylline RS in the Standard solution (mg/mL)

C_U = concentration of Theophylline in the Sample solution (mg/mL)

Acceptance criteria: See Table 2. Disregard peaks less than 0.05%.

Table 2

^a Included for establishing system suitability only.

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry at 105° for 4 h.

Acceptance criteria: The hydrous form loses 7.5%–9.5% of its weight, and the anhydrous form loses NMT 0.5% of its weight.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

Labeling: Label it to indicate whether it is hydrous or anhydrous.

USP Reference Standards 〈11〉

USP Caffeine RS

USP Theophylline RS

USP Theophylline Related Compound B RS

3-Methyl-1H-purine-2,6-dione.

C₆H₆N₄O₂ 166.14

USP Theophylline Related Compound C RS

N-(6-Amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-yl)formamide.

C₇H₁₀N₄O₂₃ 198.18

USP Theophylline Related Compound D RS

Theophyllidine;

N-Methyl-5-(methylamino)-1H-imidazole-4-carboxamide hydrochloride monohydrate.

C₆H₁₀N₄O · HCl · H₂O 208.65

USP Theophylline Related Compound F RS

Etophylline;

7-(2-Hydroxyethyl)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione.

C₉H₁₂N₄O₃ 224.22